Semiconductor memory is widely used in various electronic devices such as mobile computing devices, mobile phones, solid-state drives, digital cameras, personal digital assistants, medical electronics, servers, and non-mobile computing devices. Semiconductor memory may include non-volatile memory or volatile memory. A non-volatile memory device allows information to be stored or retained even when the non-volatile memory device is not connected to a power source.
One example of non-volatile memory uses memory cells that include reversible resistance-switching memory elements that may be set to two or more different resistance states, such as a low resistance state and a high resistance state. The memory cells may be individually connected between first and second conductors (e.g., a bit line electrode and a word line electrode). The state of such a memory cell is typically changed by proper voltages being placed on the first and second conductors. Such memory cells may be referred to herein as “resistive random access memory” (ReRAM). Since the resistivity of the memory element may be repeatedly switched between high a low resistance states, such memory cells may also be referred to as reversible resistivity memory cells.
Other non-volatile memory cells store data based on some other physical parameter. For example, some memory cells are programmed by storing charge in a charge storage region to impact a threshold voltage of the non-volatile memory cell. Such memory cells may be programmed to different threshold voltage states.
Some data stored in a storage system may be static over a long period of time. For example, a solid state drive might store data for archival purposes. Other data could be intentionally changed quite frequently. Herein, the frequency with which data is programmed is referred to as the “temperature” of the data. The more frequently the data is programmed, the hotter the data is, as defined herein.
For a variety of reasons, the state of a non-volatile memory cell is typically not permanent. For example, the resistance of a ReRAM cell may change over time. If the data stored in a group of memory cells is relatively hot, there might not be a need to refresh the data. However, for cold data, there could be a need to refresh the data at some point in time.